The need for personal wireless communications is expanding rapidly with the advances in digital communications and personal communications systems. The progress in cellular radio technology and the growth rate of the cellular telephone systems over the last several years is indicative of tremendous market demand for location independent communication via wireless access. Many of the current wireless networks architectures are primarily designed and optimized for voice communications and wide area coverage. With the proliferation of personal and portable computers, and local area networks, it is envisioned that data services and applications such as file server access, client-server execution, and electronic mail will require wireless access to the LAN environment supporting distributed computing. Since the characteristics and profile of data traffic are very different from those of voice traffic, the wireless access protocol must efficiently accommodate the very dynamic and bursty nature of data traffic.
U.S. Pat. No. 5,142,534 to Simpson et al. discloses a voice-data communication system having a base network control unit coupled to a plurality of fixed transceivers for providing communications to a plurality of portable sets. The system employs frequency hopping, time division multiplexing and demand assigned multiple access. Frequency hopping radio signals include a first set of adjacent data receiving slots, a second set of adjacent data transmitting slots and a midamble slot placed between the first and second slots. The midamble includes information for system control and signalling information used for instance for portable set registration or synchronization.
U.S. Pat. No. 5,123,029 to Bantz et al discloses a hybrid controlled access and random access scheme using frequency hopping spread spectrum communication techniques implemented in an indoor digital data radio communication system between remote stations and a computer system. A hop in the frequency hopping spread spectrum communication system is subdivided into two intervals so that different media-access protocols can be used in each interval. The protocol uses a centralized control scheme in one interval and a decentralized scheme in the other, and the intervals may be varied depending on the load of the system.
U.S. Pat. No. 4,907,224 to Scoles et al discloses a method for transmitting data in packet switching networks which provides a Collision-Eliminating Multiple Access protocol in which nodes desiring to transmit over the network channel transmit reservation requests during a plurality of contention slots, the number of contention slots being dynamically controlled according to network load. A node designated to next obtain control of the channel receives the identifiers of nodes transmitting reservation requests and, prior to transmitting application data, transmits network control data consisting of the identifiers of nodes from whom reservation requests were successfully received. The transmitted identifiers are received and stored by each node in an identical queue whereby subsequent control of the channel is rotated based on the order of node identifiers appearing on each node. The transmitted network control data includes reservation requests received during a previous contention slot period, queue correction information, and the identifiers of nodes from which the controlling node expects to receive data.
L. G. Roberts, "Dynamic Allocation of satellite capacity through packet reservation", Nat. Comput. Conf. AFIPS Conf. Proc. Vol. 42, pp. 711-716, June 1973, describes a proposal for a MAC protocol based on a reservation scheme for user data traffic and a contention scheme for making reservations.
According to the present invention, an adaptive and efficient Medium Access Control (MAC) TDMA protocol for wireless access in a local area environment is capable of supporting both bursty data traffic and synchronous services such as voice and video. Commonly used TDMA based protocol are characterized by performance limitations for sustained inbound traffic due to built-in protocol latency. The present invention overcomes such limitations by using a variable length time division frame structure with inbound and outbound traffic interleaving. A packet-switched architecture is utilized in which several remote stations within a given cell (small cells covering a range of a few hundred meters) communicate with a base station using radio channels, which can be connected to a fixed local area network. Remote stations can operate both indoor and outdoor with limited range and have wireless access to the base stations on the backbone network. As an example, consider the environment of an industrial campus consisting of several office buildings. The buildings are divided into cells, and cells are connected via some backbone network such as wired LAN. This invention addresses the intra-cell multiple access problem. The basic problem here is how to coordinate the wireless channel bandwidth which is shared by all remote stations within a cell in a fair, flexible demand-driven manner and achieve a high throughput.